Multilayer board

ABSTRACT

A multilayer board includes a laminated insulating body, signal conductors inside the laminated insulating body and extending in a transmission direction, and ground conductors sandwiching each of the signal conductors in a lamination direction via the insulating base material layers. The multilayer board includes a parallel extending portion in which the signal conductors extend parallel and that includes signal conductors arranged separately from each other in a direction orthogonal to the transmission direction in a planar view in the lamination direction, and a signal conductor overlapping with the signal conductor in a planar view in the lamination direction and arranged separately from the signal conductor in the lamination direction. The parallel extending portion includes first and second regions arranged separately in a direction orthogonal to the transmission direction in a planar view in the lamination direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-027026 filed on Feb. 16, 2017 and is a ContinuationApplication of PCT Application No. PCT/JP2018/003800 filed on Feb. 5,2018. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a multilayer board.

2. Description of the Related Art

A flat cable including multiple signal lines arranged in a widthdirection is attracting attention as a transmission line transmitting ahigh frequency signal in an electronic device. For example, WO2014/115607 describes a transmission line including a flat dielectricelement body, a signal conductor built into the dielectric element bodyand extending along a transmission direction, a reference groundconductor, an auxiliary ground conductor, and a thickness-directionconnecting conductor, and it is described that the transmission lineenables transmission with high isolation ensured between multiple highfrequency signals and can be formed compact and thin.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide multilayer boardseach including a laminated insulating body including a plurality ofinsulating base material layers that are laminated; three or more signalconductors provided inside the laminated insulating body and extendingin a transmission direction of a signal along the insulating basematerial layers; and a plurality of ground conductors sandwiching eachof the signal conductors in a lamination direction via the insulatingbase material layers. The multilayer board includes a parallel extendingportion in which the signal conductors extend parallel or substantiallyparallel to transmit a high frequency signal. The parallel extendingportion includes two or more signal conductors arranged separately fromeach other in a direction orthogonal or substantially orthogonal to thetransmission direction in a planar view in the lamination direction, anda signal conductor including an overlap with the signal conductor in aplanar view in the lamination direction and arranged separately from thesignal conductor in the lamination direction. The parallel extendingportion includes a first region and at least one second regionrespectively including the signal conductors arranged separately fromeach other in a direction orthogonal or substantially orthogonal to thetransmission direction in a planar view in the lamination direction. Thefirst region includes a larger number of overlapping signal conductorsin the lamination direction than the second region. The first regionincludes a portion in which an interval between the ground conductorssandwiching the signal conductor is smaller than a minimum value of aninterval between the ground conductors sandwiching the signal conductorin the second region.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a layer L1 of a multilayer board according toa first preferred embodiment of the present invention.

FIG. 1B is a plan view of a layer L2 of the multilayer board accordingto the first preferred embodiment of the present invention.

FIG. 1C is a plan view of a layer L3 of the multilayer board accordingto the first preferred embodiment of the present invention.

FIG. 1D is a plan view of a layer L4 of the multilayer board accordingto the first preferred embodiment of the present invention.

FIG. 1E is a plan view of a layer L5 of the multilayer board accordingto the first preferred embodiment of the present invention.

FIG. 2 is an exploded perspective view showing a structure of themultilayer board according to the first preferred embodiment of thepresent invention.

FIG. 3 is a transparent plan view of the multilayer board according tothe first preferred embodiment of the present invention.

FIG. 4 is an exemplary cross-sectional view in a parallel extendingportion of the multilayer board according to the first preferredembodiment of the present invention.

FIG. 5 is another exemplary cross-sectional view in the parallelextending portion of the multilayer board according to the firstpreferred embodiment of the present invention.

FIG. 6 is an exemplary transparent plan view of the multilayer boardincluding auxiliary ground conductors in the parallel extending portion.

FIG. 7 is another exemplary transparent plan view of the multilayerboard including auxiliary ground conductors in the parallel extendingportion.

FIG. 8 is a partially transparent plan view of the multilayer boardincluding a resist on a mounting surface as viewed from the mountingsurface side.

FIG. 9 is an exemplary cross-sectional view of the multilayer boardincluding the resist on the mounting surface.

FIG. 10 is another exemplary cross-sectional view of the multilayerboard including the resist on the mounting surface.

FIG. 11 is a schematic for explaining a mounting method of a multilayerboard including a connector on the mounting surface.

FIG. 12 is a schematic for explaining a mounting method of themultilayer board including the resist on the mounting surface.

FIG. 13 is a plan view showing an example of a mounting board with themultilayer board mounted thereon.

FIG. 14 is a side view showing another example of a mounting board withthe multilayer board mounted thereon.

FIG. 15 is a transparent plan view of a multilayer board according to asecond preferred embodiment of the present invention.

FIG. 16 is an exemplary cross-sectional view in the parallel extendingportion of the multilayer board according to the second preferredembodiment of the present invention.

FIG. 17 is an exemplary transparent plan view of the multilayer boardincluding auxiliary ground conductors in the parallel extending portion.

FIG. 18 is a transparent plan view of a multilayer board according to athird preferred embodiment of the present invention.

FIG. 19 is an exemplary cross-sectional view in the parallel extendingportion of the multilayer board according to the third preferredembodiment of the present invention.

FIG. 20 is an exemplary cross-sectional view in an end portion of theparallel extending portion of the multilayer board according to thethird preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A low-loss transmission line including more signal lines is required dueto downsizing of electronic devices in which the transmission line isused. However, if a large number of signal transmission portionsincluding signal conductors each sandwiched by ground conductors arearranged in the width direction of the transmission line, thetransmission lines are increased in width, which may make it difficultto sufficiently meet a requirement for miniaturization. According topreferred embodiments of the present disclosure, multilayer boards whichare each usable as a transmission line including multiple signaltransmission portions and capable of reducing a length in the widthdirection are able to be provided.

A multilayer board according to a first preferred embodiment includes alaminated insulating body including a plurality of insulating basematerial layers that are laminated; three or more signal conductorsprovided inside the laminated insulating body and extending in atransmission direction of a signal along the insulating base materiallayers; and a plurality of ground conductors sandwiching each of thesignal conductors in a lamination direction via the insulating basematerial layers. The multilayer board includes a parallel extendingportion in which the signal conductors extend parallel or substantiallyparallel to transmit a high frequency signal. The parallel extendingportion includes two or more signal conductors arranged separately fromeach other in a direction orthogonal or substantially orthogonal to thetransmission direction in a planar view in the lamination direction, anda signal conductor including an overlap with the signal conductor in aplanar view in the lamination direction and arranged separately from thesignal conductor in the lamination direction. The parallel extendingportion includes a first region and at least one second regionrespectively including the signal conductors arranged separately fromeach other in a direction orthogonal or substantially orthogonal to thetransmission direction in a planar view in the lamination direction. Thefirst region includes a larger number of the signal conductors arrangedto overlap in the lamination direction than the second region, and thefirst region includes a portion in which an interval between the groundconductors sandwiching the signal conductor is smaller than a minimumvalue of an interval between the ground conductors sandwiching thesignal conductor in the second region.

Since the first region includes a larger number of the signal conductorsthan the second region and the signal conductors are arranged such thatthe first region includes a portion in which an interval between theground conductors sandwiching the signal conductor is smaller than aminimum value of an interval between the ground conductors sandwichingthe signal conductor in the second region, the length in the widthdirection of the multilayer board orthogonal or substantially orthogonalto the lamination direction and the transmission direction are able tobe reduced while reducing or preventing crosstalk between the signalconductor included in the first region and the signal conductor includedin the second region.

The second region may include a signal conductor that is wider than thesignal conductor included in the first region. When the second regionincludes a wider signal conductor, even when the ground conductorinterval in the second region is wide, impedance is able to be easilymatched between signal transmission portions, and a transmission loss ofthe signal transmission portions is able to be reduced.

The parallel extending portion may include a curved portion in which thetransmission direction is bent along a plane orthogonal or substantiallyorthogonal to the lamination direction, and the first region may bedisposed at a position on the inner side relative to the second regionin the curved portion. When the first region is disposed in a portion onthe inner side of the curved portion, the line lengths of more signalconductors are able to be shortened, and the transmission loss of theentire transmission line is able to be reduced.

Lead-out conductors respectively connected to the signal conductors andled out toward a mounting surface in the lamination direction may beprovided at an end portion in the transmission direction, and the signalconductors that overlap in the lamination direction may be structuredsuch that a total length of the lead-out conductors is shorter ascompared to when the signal conductors are disposed at equal orsubstantially equal intervals in the lamination direction. Providingmore signal conductors on the mounting surface side further reduces thetransmission loss due to the lead-out conductors in the laminationdirection connected to the signal conductors.

The multilayer board may preferably further include at least oneinterlayer connection conductor connecting the ground conductors in thelamination direction, between the signal conductor included in the firstregion and the signal conductor included in the second region. Thisimproves isolation between the signal conductor included in the firstregion and the signal conductor included in the second region, so thatcrosstalk between the signal conductors is reduced or prevented. Aplurality of interlayer connection conductors may be provided along thetransmission direction. The interlayer connection conductor may be madeof a conductive paste disposed through the insulating base materiallayer or may be defined by a through hole disposed in the multilayerboard.

The multilayer board may preferably further include at least oneinterlayer connection conductor connecting the ground conductors in thelamination direction, in an outer edge portion of the parallel extendingportion. This reduces or prevents unnecessary radiation from the signalconductors to the outside. A plurality of interlayer connectionconductors may be provided along the transmission direction.

The multilayer board may preferably further include an auxiliary groundconductor disposed along the transmission direction and connected to theground conductor, between the signal conductor included in the firstregion and the signal conductor included in the second region. Thisimproves isolation between the signal conductor included in the firstregion and the signal conductor included in the second region, so thatcrosstalk between the signal conductors is effectively reduced orprevented. The auxiliary ground conductor is connected to the groundconductor by the interlayer connection conductor, for example. Theauxiliary ground conductor may preferably be a flat plate-shapedconductor, for example. The auxiliary ground conductor may be defined bya continuous flat plate-shaped conductor extending along thetransmission direction or may be defined by a plurality of flatplate-shaped conductors separated from each other along the transmissiondirection. The auxiliary ground conductor may be disposed in the same orsubstantially the same layer as the signal conductor in the laminationdirection or may be disposed in a layer different from the signalconductor. When the auxiliary ground conductor is disposed in a layerdifferent from the signal conductor in the lamination direction, aplurality of auxiliary ground conductors may be disposed in upper andlower layers sandwiching the layer in which the signal conductor isdisposed, for example.

The multilayer board may preferably further include an auxiliary groundconductor disposed along the transmission direction and connected to theground conductor, in the outer edge portion of the parallel extendingportion. This reduces or prevents unnecessary radiation from the signalconductors to the outside. The auxiliary ground conductor is preferably,for example, connected to the ground conductor by the interlayerconnection conductor. The auxiliary ground conductor is preferablyconnected to the ground conductor by the interlayer connectionconductor, for example. The auxiliary ground conductor may preferably bea flat plate-shaped conductor, for example. The auxiliary groundconductor may be defined by a continuous flat plate-shaped conductorextending along the transmission direction or may be defined by aplurality of flat plate-shaped conductors separated from each otheralong the transmission direction. The auxiliary ground conductor may bedisposed in the same or substantially the same layer as the signalconductor in the lamination direction or may be disposed in a layerdifferent from the signal conductor. When the auxiliary ground conductoris disposed in a layer different from the signal conductor in thelamination direction, a plurality of auxiliary ground conductors may bedisposed in upper and lower layers sandwiching the layer in which thesignal conductor is disposed, for example.

Preferred embodiments of the present invention will now be describedwith reference to the drawings. It is noted that the preferredembodiments described below are examples of multilayer boards todescribe the technical ideas and advantages of the present invention,and the present invention is not limited to the multilayer boardsdescribed below. The members described in claims are not limited to themembers of the preferred embodiments in any way. Particularly, thedimensions, materials, shapes, relative arrangements, and structures ofthe elements and portions described in the preferred embodiments aremerely illustrative examples and are not intended to limit the scope ofthe present invention only thereto unless otherwise specified. In thedrawings, the same or similar portions are denoted by the same referencenumerals. Although the preferred embodiments are separately describedfor convenience to facilitate explanation and/or understanding of mainpoints, configurations described in different preferred embodiments maybe partially replaced or combined. In second and subsequent preferredembodiments, matters common to the first preferred embodiment will notbe described, and only the differences will be described. Particularly,the same advantageous effects according to the same or similarconfiguration will not be described in each preferred embodiment.

First Preferred Embodiment

FIGS. 1A to 1E are plan views of respective layers L1 to L5 of amultilayer board according to a first preferred embodiment as viewedfrom the side of a surface defining and functioning as a mountingsurface. The layer L1 is on the mounting surface side, and the layers L1to L5 are laminated in this order to provide the multilayer board. Eachof the layers L1 to L5 includes a region corresponding to a parallelextending portion disposed with a ground conductor and/or a signalconductor, and a region corresponding to a lead-out portion extendingfrom the region corresponding to the parallel extending portion to aconnection terminal portion 17.

In the layer L1 of FIG. 1A, a ground conductor 12A is provided on aninsulating base material layer 11A, and the connection terminal portion17 is provided with a terminal electrode 18. For example, a connectormay be connected to the terminal electrode 18 by using solder, forexample, or the terminal electrode 18 may be directly connected to amounting electrode on a mounting board by solder, for example. Theground conductor 12A disposed in the layer L1 covers the regionscorresponding to the parallel extending portion and the lead-out portionand a region of the connection terminal portion 17 excluding a portionaround the terminal electrode 18. The terminal conductor 18 is connectedto a signal conductor built into the parallel extending portion via alead-out conductor in the transmission direction of the layer L2 and afirst interlayer connection conductor 14. If the connection conductorconnecting the terminal electrode 18 and the signal conductor isprovided on a side surface of the multilayer board, the connectionconductor allowing passage of a signal is exposed, which may adverselyaffect surrounding devices due to unnecessary radiation. In themultilayer board, the terminal electrode 18 and the signal conductor areconnected via the first interlayer connection conductor 14 disposed inthe connection terminal portion 17, and the periphery of the firstinterlayer connection conductor is surrounded by ground conductors andsecond interlayer connection conductors 15 f connecting between theground conductors. By connecting the signal conductor and the terminalelectrode 18 through the first interlayer connection conductor 14disposed inside the multilayer board in this manner, the unnecessaryradiation is able to be reduced or prevented. In this case, the firstinterlayer connection conductor may preferably have a smallercross-sectional area than a connection conductor defined by a planarconductor. Furthermore, when the first interlayer connection conductoris defined by a via conductor, for example, the via conductor ispreferably made of a material that is reactive with and capable of beingjoined to a planar conductor disposed on the insulating base materiallayer. For example, if the planar conductor is made of copper, the viaconductor is preferably made of a copper-tin-based material having alarger conductor loss than copper. From the above, the first interlayerconnection conductor with a short line length is preferably provided. Inthe layer L1, the ground conductor 12A does not cover an end surfaceportion of the insulating base material layer 11A. Therefore, when themultilayer board is made, the ground conductor 12A is not exposed on theside surface of the multilayer board and is built into a laminatedinsulating body.

The layer L2 of FIG. 1B includes a signal conductor 13A disposed on theregion corresponding to the parallel extending portion of an insulatingbase material layer 11B and lead-out conductors 16A to 16C in thetransmission direction disposed on the region corresponding to thelead-out portion. One end portion of each of the lead-out conductors 16Ato 16C in the transmission direction is connected to the terminalelectrode 18 via the first interlayer connection conductor 14 disposedin the layer L1 through the insulating base material layer 11A. Thelead-out conductor 16A is integrally provided with the signal conductor13A. The other end portion of each of the lead-out conductors 16B, 16Cis provided with a connection portion for a signal conductor 13B or 13C,and the first interlayer connection conductor 14 penetrating theinsulating base material layer 11B is connected to the connectionportion.

The region corresponding to the parallel extending portion of insulatingbase material layer 11B includes second interlayer connection conductors15 a, 15 b, and 15 d penetrating the insulating base material layer 11Band connecting the ground conductors of the layers L1, L3 to each other.A plurality of the second interlayer connection conductors 15 a areprovided along the transmission direction in an outer edge portion ofthe region corresponding to the parallel extending portion. A pluralityof the second interlayer connection conductors 15 b are provided alongthe transmission direction between the signal conductor 13A in theregion corresponding to the parallel extending portion and a regioncorresponding to the signal conductor 13B. The second interlayerconnection conductors 15 d are provided at both end portions in thetransmission direction of the region corresponding to the parallelextending portion. The isolation of the signal conductor 13A is able tobe improved by arranging the second interlayer connection conductors 15a, 15 b, and 15 d to surround the signal conductor 13A. A plurality ofsecond interlayer connection conductors 15 c are provided along thetransmission direction in an outer edge portion of the regioncorresponding to the parallel extending portion, and second interlayerconnection conductors 15 e are also provided at both end portions in thetransmission direction of the region corresponding to the parallelextending portion, so that the ground conductor 12A of the layer L1 anda ground conductor 12C of the layer L5 are connected via the secondinterlayer connection conductors 15 c or 15 e disposed in the layer L3and the layer L4. Since the ground conductors are connected through aplurality of the second interlayer connection conductors 15 a to 15 e, aground state of the multilayer board is more stabilized, and theisolation of the signal conductor is improved.

The second interlayer connection conductors 15 f are provided in anouter circumferential portion of the connection terminal portion 17 ofthe layer L2 and surrounds one end portion of each of the lead-outconductors 16A to 16C in the transmission direction. The secondinterlayer connection conductors 15 f connect the ground conductor 12Aof the layer L1 and the ground conductor 12C of the layer L5 via thesecond interlayer connection conductors 15 f provided in the layer L3and the layer L4. Since the one end portion of each of the lead-outconductors 16A to 16C in the transmission direction is surrounded by thesecond interlayer connection conductors 15 f connected to the groundconductors 12A and 12C, unnecessary radiation from the first interlayerconnection conductor 14 connected to the terminal electrode 18 isreduced or prevented. The other end portions of the lead-out conductors16B and 16C in the transmission direction are interposed between thesecond interlayer connection conductors 15 c, 15 d, and 15 e connectedto the ground conductors 12A and 12C. This reduces or preventsunnecessary radiation from the first interlayer connection conductor 14connecting the signal conductor 13B and the lead-out conductor 16B aswell as the first interlayer connection conductor 14 connecting thesignal conductor 13C and the lead-out conductor 16C.

In the layer L3 of FIG. 1C, the signal conductor 13B is provided at aposition not overlapping in the lamination direction with the signalconductor 13A of the layer L2 on the region corresponding to theparallel extending portion of an insulating base material layer 11C, anda ground conductor 12B is provided at a position overlapping in thelamination direction with the signal conductor 13A of the layer L2. Thesignal conductor 13B is connected to the lead-out conductor 16B via thefirst interlayer connection conductor 14 provided through the insulatingbase material layer 11B in the other end portion of the lead-outconductor 16B of the layer L2. As with the layer L2, a plurality of thesecond interlayer connection conductors 15 a to 15 f connecting betweenthe ground conductors are provided through the insulating base materiallayer 11C.

In the layer L4 of FIG. 1D, the signal conductor 13C is provided at aposition corresponding to the signal conductor 13A on the regioncorresponding to the parallel extending portion of an insulating basematerial layer 11D. An end portion of the signal conductor 13C isconnected to the lead-out conductor 16C via the first interlayerconnection conductor 14 provided through the insulating base materiallayer 11C in the layer L3 and the first interlayer connection conductor14 provided through the insulating base material layer 11B in the otherend portion of the lead-out conductor 16C of the layer L2. As with thelayers L2 and L3, the plurality of the second interlayer connectionconductors 15 a to 15 f connecting the ground conductors are providedthrough the insulating base material layer 11D.

In the layer L5 of FIG. 1E, the ground conductor 12C is provided on aninsulating base material layer 11E, covering the regions correspondingto the parallel extending portion and the lead-out portion as well asthe connection terminal portion 17. The ground conductor 12C isconnected to the ground conductor 12A of the layer L1 via the secondinterlayer connection conductors 15 a to 15 f provided in each of thelayers L2 to L4.

The insulating base material layers 11A to 11E are preferably made of athermoplastic resin, such as a liquid crystal polymer (LCP), forexample. The ground conductors 12A to 12C, the signal conductor 13A, thesignal conductor 13B, and the signal conductor 13C are preferably madeby, for example, a patterning process of a copper foil into a desiredshape on a single-sided copper-clad base material including the copperfoil affixed to one entire or substantially one entire surface of aninsulating base material layer. The first interlayer connectionconductor 14 and the second interlayer connection conductors 15 a to 15f may penetrate the insulating base material layer in the thicknessdirection by, for example, forming a through-hole by a method such asirradiation with a laser beam from the surface of the single-sidedcopper-clad base material not covered with the copper foil, filling thethrough-hole with a conductive paste, and solidifying the paste byheating.

FIG. 2 is an exploded perspective view showing a state of connectionbetween the layers through the first and second interlayer connectionconductors in the multilayer board according to the first preferredembodiment as viewed from the side of the surface defining andfunctioning as the mounting surface. As shown in FIG. 2 , the layers L1to L5 are laminated such that the corresponding first interlayerconnection conductors in the layers are connected to each other and thatthe corresponding second interlayer connection conductors in the layersare connected to each other, and are heated and pressurized in alamination direction by a heating press, for example, to provide themultilayer board including a laminated insulating body integrated withthe conductors. In FIG. 2 , the ground conductors 12A, 12B, and 12C areinterconnected via the plurality of the second interlayer connectionconductors 15 a to 15 e provided in the layers. To the terminalelectrode 18 disposed in the connection terminal portion 17 of the layerL1, one end portion of each of the lead-out conductors 16A, 16B, and 16Cprovided in the connection terminal portion 17 of the layer L2 isconnected via the first interlayer connection conductor 14. To the otherend portion of the lead-out conductor 16B of the layer L2, the endportion of the signal conductor 13B of the layer L3 is connected via thefirst interlayer connection conductor 14 provided in the layer L2. Tothe other end portion of the lead-out conductor 16C of the layer L2, theend portion of the signal conductor 13C of the layer L4 is connected viathe first interlayer connection conductor 14 provided in the layer L2and the first interlayer connection conductor 14 provided in the layerL3. In FIG. 2 , the state of connection of the second interlayerconnection conductors 15 f in the connection terminal portion 17 is notshown. Although the ground conductor 12A is exposed on the mountingsurface side in FIG. 2 , a resist covering the ground conductor 12A maypreferably be further provided. When the multilayer board includes aresist, the ground conductor 12A is protected from an externalenvironment, and unnecessary connection to the mounting board is reducedor prevented. The resist preferably includes an insulating resin, forexample.

FIG. 3 is a transparent plan view of a multilayer board 10 according tothe first preferred embodiment as viewed from the mounting surface side.In FIG. 3 , for simplicity, the ground conductors are not shown. Themultilayer board 10 includes a laminated insulating body 19 includingthe insulating base material layers that are laminated, and thelaminated insulating body 19 includes a parallel extending portion inwhich the signal conductors 13A, 13B, and 13C are provided, and alead-out portion including each of the lead-out conductors 16A, 16B and16C built therein and extending from the parallel extending portion tothe connection terminal portion 17. In the parallel extending portion,the signal conductors 13A, 13B, and 13C each extend in the signaltransmission direction. The signal conductors 13A and 13B are disposedseparately from each other in the width direction of the parallelextending portion orthogonal or substantially orthogonal to the signaltransmission direction as viewed in the lamination direction. The signalconductor 13C overlaps with the signal conductor 13A in the laminationdirection as viewed in the lamination direction and is disposedseparately from the signal conductor 13A in the lamination direction. InFIG. 3 , a large portion of the signal conductor 13C is hidden behindthe signal conductor 13A. In the parallel extending portion, a firstregion A including the signal conductors 13A and 13C and a second regionB including the signal conductor 13B are spaced apart from each other inthe width direction of the parallel extending portion along thetransmission direction.

The signal conductor 13A is integrated with the lead-out conductor 16Ain the transmission direction on the same surface of the insulating basematerial layer. The signal conductor 13B is connected at each of the endportions in the transmission direction via the first interlayerconnection conductor 14 to the end portion of the lead-out conductor 16Bin the parallel extending portion. The signal conductor 13C includes alead-out portion in the width direction of the parallel extendingportion at each end portion in the transmission direction and isconnected via the first interlayer connection conductor 14 in theparallel extending portion to the end portion of the lead-out conductor16C in the lead-out portion. The end portion of each of the lead-outconductors 16A, 16B and 16C in the connection terminal portion 17 isconnected to the terminal electrode 18 via the first interlayerconnection conductor 14 (not shown). The ground conductors 12A, 12B, and12C not shown are interconnected via the second interlayer connectionconductors 15 a to 15 f, and the second interlayer connection conductors15 a to 15 f provided in each of the layers are respectively connectedin the lamination direction to the second interlayer connectionconductors 15 a to 15 f disposed at corresponding positions in adjacentlayers. The plurality of the second interlayer connection conductors 15a to 15 f interconnecting the ground conductors 12A, 12B, and 12C areprovided in the outer edge portion of the parallel extending portion,between the signal conductors 13A and 13B, and in the outercircumferential portion of the connection terminal portion 17, so thatthe ground state of the multilayer board used as a high frequency signaltransmission path is stabilized.

In the multilayer board 10, the plurality of the second interlayerconnection conductors 15 a interconnecting the ground conductors 12A,12B, and 12C is provided along the transmission direction in the outeredge portion of the first region A of the parallel extending portion.Although the four second interlayer connection conductors 15 a areprovided in FIG. 3 , five or more interlayer connection conductors maybe provided. In the multilayer board 10, the plurality of the secondinterlayer connection conductors 15 c interconnecting the groundconductors 12A, 12B, and 12C is provided along the transmissiondirection in the outer edge portion of the second region B of theparallel extending portion. Although the four second interlayerconnection conductors 15 c are provided in FIG. 3 , five or moreinterlayer connection conductors may be provided. In the multilayerboard 10, the second interlayer connection conductors 15 dinterconnecting the ground conductors 12A, 12B, and 12C and the secondinterlayer connection conductors 15 e interconnecting the groundconductors 12A and 12C are provided at both end portions in thetransmission direction of the parallel extending portion. Since thesignal conductor 13A is surrounded by the ground conductors 12A and 12Bas well as the second interlayer connection conductors 15 a and 15 b,the isolation of the signal conductor 13A is able to be furtherimproved. Additionally, since the signal conductor 13B is surrounded bythe ground conductors 12A and 12C as well as the second interlayerconnection conductors 15 b and 15 c, the isolation of the signalconductor 13B is able to be improved. Furthermore, since the signalconductor 13C is surrounded by the ground conductors 12B and 12C as wellas the second interlayer connection conductors 15 a and 15 b, theisolation of the signal conductor 13C is able to be improved.

The second interlayer connection conductors 15 f are provided in theouter circumferential portion of the connection terminal portion 17 ofthe multilayer board 10 and surround the terminal electrode 18 and oneend portion of each of the lead-out conductors 16A to 16C in thetransmission direction. The second interlayer connection conductors 15 fconnect the ground conductor 12A and the ground conductor 12C in thelamination direction. Since the one end portion of each of the lead-outconductors 16A to 16C in the transmission direction is surrounded by thesecond interlayer connection conductors 15 f connected to the groundconductors 12A and 12C, the unnecessary radiation from the firstinterlayer connection conductor 14 connected to the terminal electrode18 is reduced or prevented. Additionally, the other end portions of thelead-out conductors 16B and 16C in the transmission direction areinterposed between the second interlayer connection conductors 15 c, 15d, and 15 e connected to the ground conductors 12A and 12C. This reducesor prevents the unnecessary radiation from the first interlayerconnection conductor 14 connecting the signal conductor 13B and thelead-out conductor 16B as well as the first interlayer connectionconductor 14 connecting the signal conductor 13C and the lead-outconductor 16C.

In the multilayer board 10, the plurality of the second interlayerconnection conductors 15 b interconnecting the ground conductors 12A,12B, and 12C are provided along the transmission direction between thesignal conductors 13A, 13C and the signal conductor 13B. Although thetwo second interlayer connection conductors 15 b are provided in FIG. 3, three or more second interlayer connection conductors 15 b may beprovided along the transmission direction. The plurality of the secondinterlayer connection conductors 15 b may preferably be provided in adirection orthogonal or substantially orthogonal to the transmissiondirection between the signal conductors 13A, 13C and the signalconductor 13B. This further improves both the isolation between thesignal conductor 13A and the signal conductor 13B and the isolationbetween the signal conductor 13C and the signal conductor 13B. Inaddition to the second interlayer connection conductors 15 b, anauxiliary ground conductor (not shown) extending in the transmissiondirection may preferably be provided between the signal conductors 13A,13C and the signal conductor 13B. For example, the auxiliary groundconductor is preferably defined by, for example, a flat plate-shapedconductor along the transmission direction. The auxiliary groundconductor may be provided on the layer L2 or L4 in which the signalconductor 13A or 13C is provided or may be provided between the signalconductors 13A and 13C and/or between the signal conductors 13B and 13Cin the lamination direction. A plurality of auxiliary ground conductorsmay preferably be arranged separately from each other along thetransmission direction.

In the multilayer board 10, the signal conductors and the lead-outconductors 16A to 16C in the transmission direction built into thelead-out portions are connected at the end portions of the parallelextending portion. The end portion of each of the lead-out conductors16A to 16C on the connection terminal portion 17 side is connected tothe terminal electrode 18 via the first interlayer connection conductor14. As shown in FIGS. 10 and 11 , a connector may be connected to theterminal electrode 18 using a connecting material such as solder, forexample, and may be connected to a connector on the mounting board.Alternatively, the terminal electrode 18 may be directly connected to amounting electrode on the mounting board by a connecting material, suchas solder, for example.

FIG. 4 is a cross-sectional view of the multilayer board 10 showing across section of the parallel extending portion taken along a cuttingline a-a′ of FIG. 3 with the mounting surface facing downward. In FIG. 4, a resist 19 a covering the ground conductor 12A is provided on themounting surface side of the multilayer board. The multilayer board 10includes, in the order from the side closer to the mounting surface, thesignal conductor 13A (hereinafter also referred to as a first signalconductor), the conductor 13B (hereinafter also referred to as a secondsignal conductor) provided separately from the signal conductor 13A inthe width direction of the parallel extending portion as viewed in thelamination direction, and the signal conductor 13C (hereinafter alsoreferred to as a third signal conductor) overlapping with the signalconductor 13A as viewed in the lamination direction and providedseparately therefrom in the lamination direction, disposed inside thelaminated insulating body 19. In the multilayer board 10, the signalconductors 13A, 13B, and 13C are each sandwiched between two groundconductors via the insulating base material layer. Specifically, thesignal conductor 13A is sandwiched between the ground conductors 12A and12B via the insulating base material layer, the signal conductor 13B issandwiched between the ground conductors 12A and 12C via the insulatingbase material layer, and the signal conductor 13C is sandwiched betweenthe ground conductors 12B and 12C via the insulating base materiallayer. The ground conductors 12B and 12C are built into the laminatedinsulating body 19. The ground conductor 12A is disposed on the mountingsurface side of the laminated insulating body 19 and is covered with theresist 19 a.

The parallel extending portion of the multilayer board 10 is sectionedalong the transmission direction into the first region A including alarger number of laminated signal conductors that overlap as viewed inthe lamination direction and the second region B including a smallernumber of laminated signal conductors than the first region A. Althoughthe number of signal conductors arranged separately from each other inthe width direction of the parallel extending portion is two in FIG. 4 ,three or more signal conductors may be arranged separately from eachother in the width direction. In this case, the first region A is aregion including the largest number of laminated signal conductors thatoverlap, and the second region B is each of the regions including thesignal conductors arranged separately in the width direction from thesignal conductors included in the first region A. In FIG. 4 , the firstsignal conductor 13A and the third signal conductor 13C are arrangedsuch that a width of an overlapping portion coincides with therespective line widths as viewed in the lamination direction. However,the signal conductors may be structured such that the width of theoverlapping portion is narrower than the line width of any of the signalconductors.

In the multilayer board 10, an interval between the ground conductors12A and 12B sandwiching the first signal conductor 13A and an intervalbetween the ground conductors 12B and 12C sandwiching the third signalconductor 13C included in the first region A are narrower than aninterval between the ground conductors 12A and 12C sandwiching thesecond signal conductor 13B in the second region B. In the multilayerboard 10, if the second region B includes a plurality of second signalconductors 13B that overlap in the lamination direction, the firstregion A includes a signal conductor sandwiched by ground conductors atan interval narrower than the minimum value of the interval of theground conductors sandwiching the second signal conductors 13B.

In the multilayer board 10, the line width of the signal conductor 13Bincluded in the second region B is wider than the line width of any ofthe first signal conductor 13A and the third signal conductor 13Bincluded in the first region A. By providing the wider line width of thesignal conductor 13B sandwiched by the ground conductors at a widerinterval, impedance is able to be easily matched with a signaltransmission portion having a narrow ground conductor interval. Themultilayer board 10 used as a transmission line is generally designedwith a characteristic impedance of about 50Ω, for example. By making theline width of the second signal conductor 12B wider, the samecharacteristic impedance of about 50Ω is able to be achieved in a firstsignal transmission portion including the first signal conductor 13A,the ground conductor 12A, and the ground conductor 12B and a thirdsignal transmission portion including the third signal conductor 13C,the ground conductor 12B, and the ground conductor 12C, as well as asecond signal transmission portion including the second signal conductor13B, the ground conductor 12A, and the ground conductor 12C. A signalpassing through the second signal conductor 13B having the larger linewidth is reduced in conductor loss as compared to a signal passingthrough the first signal conductor 13A or the third signal conductor13C. Therefore, for example, if a signal of about 600 MHz to about 900MHz band or about 2 GHz band, for example, used for cellular phones isassigned to a first signal transmission portion or a third signaltransmission portion, for example, a signal of about 5 GHz band used forWiFi is preferably assigned to a signal transmission portion. In otherwords, it is preferable to assign a signal of a high frequency band,which is more significantly affected by transmission loss, to a secondsignal transmission portion including the signal conductor with a widerline width. Instead of making the line width of the signal conductorwider, the signal conductor may be made thicker to adjust thecharacteristic impedance. For example, the second signal conductor 13Bmay be thicker than the first signal conductor 13A or the third signalconductor 13C to match the impedance. However, a process ofmanufacturing the multilayer board 10 used as a transmission line may besimplified by making the second signal conductor 13B wider to match theimpedance.

In the multilayer board 10, the ground conductors 12A, 12B, and 12C areprovided along the transmission direction of the signal conductors. Theground conductors 12A, 12B, and 12C are connected to each other sincethe second interlayer connection conductors 15 a to 15 f providedthrough the insulating base material layer are connected in thelamination direction. In FIG. 4 , the ground conductors 12A and 12C areconnected to each other via the second interlayer connection conductors15 a and 15 c provided in the outer edge portion of the parallelextending portion and the signal interlayer connection conductor 15 bprovided between the first signal conductor and the third signalconductor. The ground conductor 12B is connected to the groundconductors 12A and 12C via the second interlayer connection conductor 15a provided in the outer edge portion of the parallel extending portionand the second interlayer connection conductor 15 b provided between thefirst signal conductor and the third signal conductor.

FIG. 5 is a cross-sectional view of the multilayer board 10 includingauxiliary ground conductors extending in the transmission directionprovided between the signal conductors 13A, 13C and the signal conductor13B, showing a cross section of the parallel extending portioncorresponding to the cutting line a-a′ of FIG. 3 with the mountingsurface facing downward. In FIG. 5 , the resist 19 a covering the groundconductor 12A is disposed on the mounting surface side of the multilayerboard. In FIG. 5 , an auxiliary ground conductor 12D connected to thesecond interlayer connection conductor 15 b is disposed between thesignal conductors 13A and 13B separately from each of the signalconductors 13A and 13B in the width direction of the parallel extendingportion and the lamination direction. An auxiliary ground conductor 12Econnected to the second interlayer connection conductor 15 b is disposedbetween the signal conductors 13B and 13C separately from the signalconductors 13B and 13C in the width direction of the parallel extendingportion and the lamination direction. By providing the auxiliary groundconductor 12D, the isolation between the signal conductors 13A and 13Bis able to be further improved. By providing the auxiliary groundconductor 12E, the isolation between the signal conductors 13C and 13Bis able to be further improved. The auxiliary ground conductors 12D and12E preferably have a flat plate shape extending in the transmissiondirection, for example.

FIG. 6 is an exemplary transparent plan view of the parallel extendingportion of the multilayer board 10 including the auxiliary groundconductors 12D and 12E connected to the second interlayer connectionconductor 15 b as viewed from the mounting surface side. In FIG. 6 , forsimplicity, the ground conductors 12A, 12B, and 12C are not shown. InFIG. 6 , the auxiliary ground conductor 12D connected to the secondinterlayer connection conductors 15 b is provided inside the laminatedinsulating body 19 defined by a flat plate-shaped conductor continuouslyextended in the transmission direction between the signal conductors 13Band 13A. The auxiliary ground conductor 12E is hidden behind theauxiliary ground conductor 12D. The auxiliary ground conductor 12D isconnected to the second interlayer connection conductor 15 a via theground conductors 12A, 12B, and 12C not shown and is connected to thesecond interlayer connection conductors 15 c, 15 d, and 15 e via theground conductors 12A and 12C. In a planar view, the signal conductor13A is surrounded by the auxiliary ground conductor 12D and the secondinterlayer connection conductors 15 a and 15 b, and the signal conductor13B is surrounded by the auxiliary ground conductor 12D and the secondinterlayer connection conductors 15 b and 15 c. The auxiliary groundconductors 12D and 12E may have the same width or different widths.

FIG. 7 is another exemplary transparent plan view of the parallelextending portion of the multilayer board 10 including the auxiliaryground conductors 12D and 12E connected to the second interlayerconnection conductors 15 b as viewed from the mounting surface side. InFIG. 7 , for simplicity, the ground conductors 12A, 12B, and 12C are notshown. In FIG. 7 , the auxiliary ground conductors 12D respectivelyconnected to the second interlayer connection conductors 15 b areprovided inside the laminated insulating body 19 defined by rectangularor substantially rectangular flat plates provided separately from eachother in the transmission direction between the signal conductors 13Band 13A. The auxiliary ground conductors 12E are hidden behind theauxiliary ground conductors 12D. In a planar view, the signal conductor13A is surrounded by the auxiliary ground conductors 12D and the secondinterlayer connection conductors 15 a and 15 b, and the signal conductor13B is surrounded by the auxiliary ground conductors 12D and the secondinterlayer connection conductors 15 b and 15 c. The auxiliary groundconductors 12D preferably have a rectangular or substantiallyrectangular shape in FIG. 7 or may have a polygonal shape, a circularshape, an elliptical shape, an oval shape, etc. The auxiliary groundconductors 12D and 12E may have the same shape or different shapes.

FIG. 8 is a partially transparent plan view of the multilayer board 10on which the resist 19 a covering the ground conductor 12A is providedon the mounting surface side as viewed from the mounting surface side.The ground conductors 12A and 12C are not shown in a transparentportion. In FIG. 8 , in the connection terminal portion 17, the terminalelectrode 18, and ground electrodes 18 a surrounding the terminalelectrode 18 are exposed from opening portions of the resist 19 a. Theground electrodes 18 a are exposed surfaces of the ground conductor 12Ain the opening portions of the resist 19 a, for example.

FIG. 9 is a cross-sectional view of the multilayer board 10 includingthe resist 19 a on the mounting surface side taken along a line a-a′ ofFIG. 8 and is a cross-sectional view taken with the mounting surfacefacing upward. In FIG. 9 , the ground conductor 12C built into thelaminated insulating body 19 and the ground conductor 12A disposed onthe surface of the laminated insulating body 19 on the mounting surfaceside are continuously disposed in the lead-out portion and the parallelextending portion. The resist 19 a is disposed on the surface of theground conductor 12A on the mounting surface side. The ground conductors12A and 12C are connected, together with the ground conductor 12Bdisposed therebetween, in the lamination direction via the secondinterlayer connection conductor 15 b. The ground conductor 12B isprovided in the same layer as the signal conductor 13B (not shown)included in the second region. The ground conductor 12B and the groundconductor 12A sandwich the signal conductor 13A provided in the samelayer as the lead-out conductor 16C in the transmission direction in thefirst region. The ground conductor 12B and the ground conductor 12Csandwich the signal conductor 13C in the first region. This improves theisolation between the signal conductors and reduces or preventscrosstalk.

The lead-out conductor 16C in the transmission direction disposed in thelead-out portion is sandwiched between the ground conductors 12A and12C, so that unnecessary radiation to the outside is reduced orprevented. The end portion of the lead-out conductor 16C on theconnection terminal portion 17 side is connected to the terminalelectrode 18 disposed on the mounting surface via the first interlayerconnection conductor 14 disposed through the insulating base materiallayer. The resist 19 a is not disposed on a portion of the surface ofthe terminal electrode 18 on the mounting surface side, and the surfaceis exposed on the mounting surface side. The ground electrodes 18 a areprovided around the terminal electrode 18 as exposed portions of theground conductor 12A in the opening portions of the resist 19 a. Theother end portion of the lead-out conductor 16C on the side opposite tothe connection terminal portion 17 is connected to the end portion ofthe signal conductor 12C via the first interlayer connection conductor14 disposed in the lamination direction through the insulating basematerial layer.

FIG. 10 is a cross-sectional view of the multilayer board 10 includingconnectors 18 b on the connection terminal portion 17 corresponding tothe line a-a′ of FIG. 8 and is a cross-sectional view taken with themounting surface facing upward. In FIG. 10 , the resist 19 a coveringthe ground conductor 12A is disposed on the mounting surface side. Theconnectors 18 b are each disposed on the resist 19 a of the connectionterminal portion 17, and the terminal electrode 18 exposed from theresist 19 a and the exposed portions of the ground conductor 12A in theopening portions of the resist 19 a are connected respectively viaconnection materials 18 c to the connector 18 b. For example, solder maypreferably be used for the connection materials 18 c. The connector 18 bis connected via the connection material 18 c, the terminal electrode18, the first interlayer connection conductor 14, and the lead-outconductor 16C to the signal conductor 13C and is connected via theconnection material 18 c to the ground conductor 12A.

FIG. 11 is a schematic cross-sectional view for explaining a method ofmounting the multilayer board 10 including the connectors 18 b in theconnection terminal portion 17 onto a mounting board 100. Each of theconnectors 18 b of the multilayer board 10 is connected via theconnection material 18 c, the terminal electrode 18, the firstinterlayer connection conductor 14, and the lead-out conductor 16C tothe signal conductor 13C. Each of the connectors 18 b is connected viathe connection material 18 c to the exposed portions of the groundconductor 12A in the opening portions of the resist 19 a. The mountingboard 100 includes a resist 102 disposed on an insulating base materiallayer 101 and partially exposing terminal portions 103 a and 103 b. Theterminal portions 103 a and 103 b are connected via connection materialsnot shown to connectors 104 a and 104 b, respectively. The terminalportions 103 a and 104 b each include a signal terminal and a groundterminal, for example. The two connectors 18 b of the multilayer board10 are respectively connected to the connectors 104 a and 104 b of themounting board 100, so that the multilayer board 10 is mounted on themounting board 100. When the multilayer board 10 is mounted on themounting board 100, the signal terminal of 103 a of the mounting board100 is connected sequentially via the connector 104 a, the connector 18b, the connection material 18 c, the terminal electrode 18, the firstinterlayer connection conductor 14, the lead-out conductor 16C, and thefirst interlayer connection conductor 14 to one end portion of thesignal conductor 13C. The other end portion of the signal conductor 13Cis connected sequentially via the first interlayer connection conductor14, the lead-out conductor 16C, the first interlayer connectionconductor 14, the terminal electrode 18, the connection material 18 c,the connector 18 b, and the connector 104 b to the signal terminal of103 b of the mounting board 100. As a result, the signal terminal of theterminal portion 103 a and the signal terminal of the terminal portion103 b of the mounting board 100 are connected to the multilayer board10. The ground terminals of 103 a and 103 b of the mounting board 100are connected sequentially via the connector 104 a, the connector 18 b,and the connection material 18 c to the ground electrode 18 a integrallyformed with the ground conductor 12A. Therefore, a signal is transmittedbetween the terminal portions 103 a and 103 b of the mounting board 100to the multilayer board 10.

FIG. 12 is a schematic cross-sectional view for explaining anotherexample of the method of mounting the multilayer board 10 onto themounting board 100. The mounting board 100 includes the resist 102disposed on the insulating base material layer 101 and partiallyexposing signal terminals 103 a 1 and 103 a 2 and ground terminals 103 b1 and 103 b 2. Connection materials 105 are respectively disposed on thesignal terminals 103 a 1 and 103 a 2 and the ground terminals 103 b 1and 103 b 2. For example, solder is preferably used for the connectionmaterials 105. The terminal electrodes 18 and the ground electrodes 18 aof the connection terminal portions 17 are connected via the connectionmaterials 105 to the signal terminals and the ground terminals of themounting board, so that the multilayer board 10 is mounted on themounting board. When the multilayer board 10 is mounted on the mountingboard 100, the signal terminal of 103 a 1 of the mounting board 100 isconnected sequentially via the connection material 105, the terminalelectrode 18, the first interlayer connection conductor 14, the lead-outconductor 16C, and the first interlayer connection conductor 14 to oneend portion of the signal conductor 13C. The other end portion of thesignal conductor 13C is connected sequentially via the first interlayerconnection conductor 14, the lead-out conductor 16C, the firstinterlayer connection conductor 14, the terminal electrode 18, and theconnection material 105 to the signal terminal 103 a 2 of the mountingboard 100. As a result, the signal terminal 103 a 1 and the signalterminal 103 a 2 of the mounting board 100 are connected to themultilayer board 10. The ground terminals 103 b 1 and 103 b 2 of themounting board 100 are respectively connected via the connectionmaterials 105 to the ground electrodes 18 a that are exposed portions ofthe ground conductor 12A in the opening portions of the resist 19 a ofthe multilayer board 10.

FIG. 13 is a plan view schematically showing a mounting state of themultilayer board 10 on the mounting board 100. The multilayer board 10and other electronic components 110 are provided on the mounting board100. The electronic components 110 include chip components, such asintegrated circuits (ICs), resistors, capacitors, and inductors, forexample. The multilayer board 10 includes connection terminal portions17 a 1, 17 b 1, 17 c 1, 17 a 2, 17 b 2, and 17 c 2 respectivelyconnected to terminal portions on the mounting board and is thus mountedon the mounting board. The connection terminal portions are connected tothe terminal portions on the mounting board through connectors or aconnection material, such as solder, for example. For example, theterminal portion connected to the terminal portion 17 a 1 of themultilayer board 10 is connected to the terminal portion connected tothe terminal portion 17 a 2 via the multilayer board 10, and theterminal portion connected to the terminal portion 17 b 1 of themultilayer board 10 is connected to the terminal portion 17 b 2 via themultilayer board 10, and the terminal portion connected to the terminalportion 17 c 1 of the multilayer board 10 is connected to the terminalportion connected to the terminal portion 17 c 2 via the multilayerboard 10.

FIG. 14 is a plan view schematically showing the mounting board 100including the multilayer board 10 mounted thereon and housed in ahousing 120. In FIG. 14 , the connectors 18 b provided on the connectionterminal portions 17 of the multilayer board 10 are respectivelyconnected to the connectors 104 a and 104 b provided on the mountingboard 100, so that the multilayer board 10 is mounted on the mountingboard 100 over the electronic component 110. The multilayer board 10 isthen housed in the housing 120. The multilayer board 10 includes thesignal conductors provided in the first and second regions in the widthdirection of the parallel extending portion. As a result, the thicknessof the entire multilayer board 10 is able to be thinner as compared towhen all of the signal conductors are provided in the laminationdirection. Therefore, by using a flexible base material, such as aliquid crystal polymer (LCP), for example, for the insulating basematerial layer of the multilayer board 10, the multilayer board 10 isable to be bent and disposed depending on a shape of a gap between themounting board 100 including the electronic components 110 providedthereon and the housing 120.

Second Preferred Embodiment

FIG. 15 is a transparent plan view of a multilayer board 20 according toa second preferred embodiment of the present invention as viewed fromthe mounting surface side. In FIG. 15 , for simplicity, the groundconductors are not shown. The multilayer board 20 of the secondpreferred embodiment has the same or substantially the sameconfiguration as the multilayer board of the first preferred embodimentexcept that the multilayer board includes a curved portion C with atransmission direction that is bent along a plane orthogonal orsubstantially orthogonal to the lamination direction in the parallelextending portion and that the first region is disposed at an innerposition in the curved portion C. The multilayer board having the curvedportion in the parallel extending portion is mounted to detour aroundthe electronic component 110 of FIG. 13 , for example.

In the multilayer board 20, signal conductors 23A, 23B, and 23C extendin the transmission direction inside a laminated insulating body 29. Thesignal conductors 23A and 23B are arranged separately from each other inthe width direction of the parallel extending portion orthogonal orsubstantially orthogonal to the signal transmission direction. Thesignal conductor 23C overlaps with the signal conductor 23A in thelamination direction and is disposed separately from the signalconductor 23A in the lamination direction. In the multilayer board 20,the first region including a larger number of signal conductorslaminated to overlap as viewed in the lamination direction is disposedat a position on the inner side relative to the second region in thecurved portion C. In FIG. 15 , the first region includes the signalconductors 23A and 23C, and the second region includes the signalconductor 23B. The first region and the second region are sectioned inthe width direction of the parallel extending portion along thetransmission direction.

In FIG. 15 , a plurality of second interlayer connection conductors 25 binterconnecting ground conductors not shown are provided along thetransmission direction between the signal conductors 23A, 23C and thesignal conductor 23B. Additionally, a plurality of second interlayerconnection conductors 25 a and 25 c interconnecting the groundconductors are provided along the transmission direction in the outeredge portion of the parallel extending portion. By providing theplurality of the second interlayer connection conductors 25 a and 25 calong the transmission direction in the outer edge portion of theparallel extending portion, unnecessary radiation from the signalconductors to the outside is able to be effectively reduced orprevented. Particularly, since the plurality of the second interlayerconnection conductors 25 a are provided in the outer edge portion of theparallel extending portion on the inner side of the curved portion C ofthe multilayer board 20, an influence of crosstalk, for example, is ableto be more effectively reduced or prevented from occurring due tounnecessary radiation between different positions of the adjacent signalconductors on the inner side of the curved portion C. Although the samenumbers of the second interlayer connection conductors 25 a, 25 b, and25 c are provided along the transmission direction in FIG. 15 , thesecond interlayer connection conductors 25 a, 25 b, and 25 c may beprovided in respective different numbers. For example, the number of thesecond interlayer connection conductors 25 a provided on the inner sideof the curved portion C may be larger or smaller than the number of thesecond interlayer connection conductors 25 c provided on the outer sideof the curved portion C. The second interlayer connection conductors 25a, 25 b, and 25 c may respectively be arranged at equal or substantiallyequal intervals.

Furthermore, the multilayer board 20 may include an auxiliary groundconductor (not shown) extending in the transmission direction, inaddition to the ground conductors and the second interlayer connectionconductors 25 a to 25 c. By including the auxiliary ground conductor,the isolation between the signal conductors is able to be furtherimproved. For example, the auxiliary ground conductor may preferably bea continuous flat plate-shaped conductor along the transmissiondirection or may be flat plate-shaped conductors separated from eachother along the transmission direction.

A cross-sectional view of the multilayer board 20 showing a crosssection of the parallel extending portion taken along a cutting lineb-b′ of FIG. 15 with the mounting surface facing downward is the same asFIG. 4 . In the multilayer board 20, an interval between the two groundconductors sandwiching the signal conductor included in the first regionA is preferably smaller than an interval between the two groundconductors sandwiching the signal conductor in the second region B.Since the signal conductors included in the first region A on the innerside of the curved portion C are sandwiched by the ground conductors atnarrow intervals, an influence of crosstalk, for example, is able to beeffectively reduced or prevented from occurring due to unnecessaryradiation between different positions of the adjacent signal conductorson the inner side of the curved portion C.

FIG. 16 is a cross-sectional view of the multilayer board 20 includingauxiliary ground conductors extending in the transmission directiondisposed between the signal conductors 23A, 23C and the signal conductor23B and in the outer edge portion of the parallel extending portion,showing a cross section of the parallel extending portion correspondingto the cutting line b-b′ of FIG. 15 with the mounting surface facingdownward. The multilayer board 20 includes, in the order from the sidecloser to the mounting surface, the signal conductor 23A, the conductor23B disposed separately from the signal conductor 23A in the widthdirection of the parallel extending portion as viewed in the laminationdirection, and the signal conductor 23C including an overlap with thesignal conductor 23A as viewed in the lamination direction and disposedseparately therefrom in the lamination direction, provided inside thelaminated insulating body 29. In the multilayer board 20, the signalconductor 23A is sandwiched between ground conductors 22A and 22B viathe insulating base material layer, the signal conductor 23B issandwiched between ground conductors 22A and 22C via the insulating basematerial layer, and the signal conductor 23C is sandwiched between theground conductors 22B and 22C via the insulating base material layer.The ground conductors 22B and 22C are built into the laminatedinsulating body 29, and the ground conductor 22A is disposed on thesurface on the mounting surface side of the laminated insulating body29. In FIG. 16 , a resist 29 a covering the ground conductor 22A isprovided on the mounting surface side of the laminated insulating body29.

In FIG. 16 , an auxiliary ground conductor 22D2 connected to the secondinterlayer connection conductor 25 b is disposed between the signalconductors 23A and 23B separately from the signal conductors 23A and 23Bin the width direction of the parallel extending portion and thelamination direction. An auxiliary ground conductor 22E2 connected tothe second interlayer connection conductor 25 a is disposed between thesignal conductors 23B and 23C separately from the signal conductors 23Band 23C in the width direction of the parallel extending portion and thelamination direction. In the outer edge portion of the first region A,auxiliary ground conductors 22D1 and 22E1 connected to the secondinterlayer connection conductor 25 a are provided with the groundconductor 22B interposed between the signal conductors 23A and 23C. Inthe outer edge portion of the second region B, auxiliary groundconductors 22D3 and 22E3 connected to the second interlayer connectionconductor 25 c are disposed separately from each other in the laminationdirection. Since the auxiliary ground conductors 22D1, 22E1, 22D3, and22E32 are provided in the outer edge portion of the parallel extendingportion, the unwanted radiation from the signal conductors 23A, 23B, and23C to the outside is able to be more effectively reduced or prevented.Particularly, since the auxiliary ground conductors 22D1 and 22E1 areprovided on the inner side of the curved portion C, an influence ofcrosstalk, for example, is able to be effectively reduced or preventedfrom occurring due to unnecessary radiation between different positionsof the adjacent signal conductors on the inner side of the curvedportion C.

FIG. 17 is an exemplary transparent plan view of the parallel extendingportion of the multilayer board 20 including the auxiliary groundconductors 22D1 to 22D3 and 22E1 to 22E3 connected to the secondinterlayer connection conductor 25 b as viewed from the mounting surfaceside. In FIG. 17 , for simplicity, the ground conductors 12A, 12B, and12C are not shown. In FIG. 17 , the auxiliary ground conductors 22D1connected to the second interlayer connection conductor 25 a arepreferably oblong flat plate-shaped conductors separately from eachother along the transmission direction in the outer edge portion of theparallel extending portion inside the laminated insulating body 29. Theauxiliary ground conductors 22E1 are hidden behind the auxiliary groundconductors 22D2. The auxiliary ground conductors 22D2 connected to thesecond interlayer connection conductor 25 a are preferably oblong flatplate-shaped conductors provided separately from each other along thetransmission direction between the signal conductors 23B and 23A. Theauxiliary ground conductors 22E2 are hidden behind the auxiliary groundconductors 22D2. The auxiliary ground conductors 22D3 connected to thesecond interlayer connection conductor 25C are preferably oblong flatplate-shaped conductors separately from each other along thetransmission direction in the outer edge portion of the parallelextending portion. The auxiliary ground conductors 22D1, 22D2, and 22D3are interconnected via the ground conductors 22A, 22B, and 22C notshown. In a planar view, the signal conductor 23A is surrounded by theauxiliary ground conductors 22D1 and 22D2, and the signal conductor 13Bis surrounded by the auxiliary ground conductors 22D2 and 22D3. Theauxiliary ground conductors 22D1 and 22D3 preferably have the same orsubstantially the same width, which is different from the width of theauxiliary ground conductor 22D2.

Third Preferred Embodiment

FIG. 18 is a transparent plan view of a multilayer board 30 according toa third preferred embodiment of the present invention as viewed from themounting surface side. In FIG. 18 , for simplicity, the groundconductors are not shown. The multilayer board 30 of the third preferredembodiment has the same or substantially the same configuration as themultilayer board of the first preferred embodiment except that the firstregion includes four signal conductors while the second region includesthree signal conductors and that signal conductors that overlap in thelamination direction are provided such that a total length of lead-outconductors in the lamination direction is shorter as compared to whenthe signal conductors are arranged at equal or substantially equalintervals in the lamination direction.

The parallel extending portion of the multilayer board 30 is sectionedin the width direction of the parallel extending portion along thetransmission direction into a first region including signal conductors33A, 33C1, 33C2, and 33C3 and a second region including signalconductors 33B1, 33B2, and 33B3.

The signal conductor 33A is integral with a lead-out conductor in thetransmission direction on the same surface of the insulating basematerial layer. The signal conductors 33B1 to 33B3 are connected atrespective end portions in the transmission direction via firstinterlayer connection conductors 34 respectively to end portions oflead-out conductors in the parallel extending portion. The signalconductors 33C1 to 33C3 include lead-out portions in the width directionof the parallel extending portion at respective end portions in thetransmission direction and are connected at the lead-out portions viathe first interlayer connection conductors 34 to the end portions oflead-out conductors in the parallel extending portion.

FIG. 19 is a cross-sectional view of the multilayer board 30 showing across section of the parallel extending portion taken along a cuttingline c-c′ of FIG. 18 with the mounting surface facing downward. In FIG.19 , no resist covering the ground conductor 32A is provided on themounting surface side of the laminated insulating body. The multilayerboard 30 includes the first region A in which the signal conductor 33A(hereinafter also referred to as a first signal conductor) and thesignal conductors 33C1 to 33C3 (hereinafter all also referred to asthird signal conductors) arranged separately from each other in thelamination direction are provided in the order from the side closer tothe mounting surface inside the laminated insulating body 19. In thesecond region B, the signal conductors 33B1 to 33B3 (hereinafter allalso referred to as second signal conductors) are provided in the orderfrom the side closer to the mounting surface inside the laminatedinsulating body 19. The second signal conductors 33B1 to 33B3 arearranged separately from the signal conductor 33A in the width directionof the parallel extending portion when viewed in the laminationdirection. The third signal conductors 33C1 to 33C3 overlap with thesignal conductor 33A when viewed in the lamination direction.

In FIG. 19 , an interval between the ground conductors 32A and 32Bsandwiching the first signal conductor 33A and an interval between theground conductors 32B and 32C sandwiching the third signal conductor33C1 are narrower than an interval between the ground conductors 32A and32C sandwiching the second signal conductor 33B1. The line widths of thesecond signal conductors 33B1 to 33B3 included in the second region Bare wider than the line widths of the first signal conductor 33A and thethird signal conductors 33C1 to 33C3 included in the first region A.

In the first region A of the multilayer board 30, the signal conductorsarranged along the lamination direction are provided at a higher densityon the mounting surface side. Specifically, when the multilayer board 30is divided into two regions by a plane passing through a middle point ofthe thickness thereof and orthogonal or substantially orthogonal to thethickness direction, the number of signal conductors included in theregion on the mounting surface side is larger than a number of signalconductors included in the region on the side opposite to the mountingsurface side.

FIG. 20 is a cross-sectional view of the multilayer board 30 showing across section of the parallel extending portion taken along a cuttingline d-d′ of FIG. 18 with the mounting surface facing downward. In FIG.20 , no resist covering the ground conductor 32A is provided on themounting surface side of the laminated insulating body. In themultilayer board 30, the end portions of the signal conductors 33B1 to33B3 and 33C1 to 33C3 are respectively connected via the firstinterlayer connection conductors 34 extending along the laminationdirection from the signal conductors toward the mounting surface to theend portion of the lead-out conductors 36B1 to 36B3 and 36C1 to 36C3 inthe transmission direction in the parallel extending portion. The firstinterlayer connection conductors 34 are provided such that the firstinterlayer connection conductors provided through the insulating basematerial layers are connected between the layers in the laminationdirection.

In the second region B of FIG. 20 , the signal conductors 33B1 to 33B3are arranged at equal or substantially equal intervals in the laminationdirection. In the first region A, the signal conductors 33A and 33C1 to33C3 are provided such that the total length of the first interlayerconnection conductors 34 is shorter as compared to when the signalconductors are arranged at equal or substantially equal intervals in thelamination direction.

The ground conductors are connected by the second interlayer connectionconductors provided through the insulating base material layers in thepreferred embodiments described above or may be connected bythrough-holes, instead of the interlayer connection conductors. Theground conductors may be connected by a side conductor layer disposedalong the lamination direction at end portions in the width direction inthe parallel extending portion. The side conductor layer is disposed atboth end portions in the width direction, for example. The groundconductors and the side conductor layer may be connected by extendingthe ground conductors to the end portions in the width direction or maybe connected by providing lead-out conductors from the ground conductorsto the end portions in the width direction. The side conductor layer maybe provided by plating on the side surface of the multilayer board, forexample. Furthermore, the side conductor layer may be provided on theentire or substantially the entire side surface of the parallelextending portion along the transmission direction or may be defined bya plurality of side conductor layers arranged separately from each otheralong the transmission direction and extend along the laminationdirection.

The multilayer boards according to the preferred embodiments describedabove are each used as a transmission line for high frequency signals.Although the application of the first and third signal conductors andthe second signal conductor included in the multilayer board is notparticularly limited, for example, the second signal conductor may bemade wider than the first and third signal conductors and is thereforesuitable for signal transmission in which a lower loss is required, forexample, signal transmission in a higher frequency band. On the otherhand, the first signal conductor and the third signal conductor aresandwiched between the ground conductors at a narrower interval and aretherefore suitable for signal transmission in which more isolation isrequired, for example, signal transmission in a lower frequency band.

All the documents, patent applications, and technical standardsdescribed in this description are hereby incorporated by reference tothe same extent as if each of the documents, patent applications, andtechnical standards is specifically and individually described as beingincorporated by reference.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multilayer board comprising: a laminatedinsulating body including a plurality of insulating base material layersthat are laminated; three or more signal conductors provided inside thelaminated insulating body and extending in a transmission direction of asignal along the plurality of insulating base material layers; and aplurality of ground conductors sandwiching each of the three or moresignal conductors in a lamination direction via the plurality ofinsulating base material layers; wherein the multilayer board includes aparallel extending portion in which the three or more signal conductorsextend parallel to transmit a high frequency signal; the parallelextending portion includes two or more signal conductors of the three ormore signal conductors arranged separately from each other in adirection orthogonal or substantially orthogonal to the transmissiondirection in a planar view in the lamination direction, and at least oneother signal conductor of the three or more signal conductors thatoverlaps with at least one of the two or more signal conductors in theplanar view in the lamination direction and is arranged separately fromthe two or more signal conductors in the lamination direction; theparallel extending portion includes a first region and at least onesecond region respectively including the two or more signal conductorsarranged separately from each other in the direction orthogonal orsubstantially orthogonal to the transmission direction in the planarview in the lamination direction; a number of the signal conductors ofthe three or more signal conductors in the first region that overlap inthe lamination direction is larger than a number of the signalconductors of the three or more signal conductors in the at least onesecond region that overlap in the lamination direction; the first regionincludes a portion in which an interval between the plurality of groundconductors sandwiching the signal conductors of the three or more signalconductors is smaller than a minimum value of an interval between theplurality of ground conductors sandwiching the signal conductors of thethree or more signal conductors in the at least one second region; andin the first region, the signal conductors of the three or more signalconductors provided along the lamination direction are provided at ahigher density on a mounting surface side.
 2. The multilayer boardaccording to claim 1, wherein the signal conductors of the three or moresignal conductors in the at least one second region are wider than thesignal conductors of the three or more signal conductors in the firstregion.
 3. The multilayer board according to claim 1, wherein lead-outconductors respectively connected to the three or more signal conductorsand led out toward a mounting surface in the lamination direction areprovided at an end portion in the transmission direction; and the threeor more signal conductors that overlap in the lamination direction arearranged such that a total length of the lead-out conductors is shorterthan a structure in which the three or more signal conductors arearranged at equal or substantially equal intervals in the laminationdirection.
 4. The multilayer board according to claim 3, wherein thelead-out conductors are respectively integrated with the three or moresignal conductors.
 5. The multilayer board according to claim 1, furthercomprising at least one interlayer connection conductor connecting theplurality of ground conductors in the lamination direction, between thesignal conductors of the three or more signal conductors included in thefirst region and the signal conductors of the three or more signalconductors included in the at least one second region.
 6. The multilayerboard according to claim 5, wherein the at least one interlayerconnection conductor is defined by a via conductor.
 7. The multilayerboard according to claim 6, wherein the via conductor is made of acopper-tin-based material.
 8. The multilayer board according to claim 1,further comprising at least one interlayer connection conductorconnecting the plurality of ground conductors in the laminationdirection, in an outer edge portion of the parallel extending portion.9. The multilayer board according to claim 8, wherein each of the threeor more signal conductors is surrounded by the plurality of groundconductors and the at least one interlayer connection conductor.
 10. Themultilayer board according to claim 8, wherein the at least oneinterlayer connection conductor is defined by a via conductor.
 11. Themultilayer board according to claim 10, wherein the via conductor ismade of a copper-tin-based material.
 12. The multilayer board accordingto claim 1, further comprising an auxiliary ground conductor disposedalong the transmission direction and connected to the plurality ofground conductors, between the signal conductors of the three or moresignal conductors included in the first region and the signal conductorsof the three or more signal conductors included in at least one thesecond region.
 13. The multilayer board according to claim 1, furthercomprising an auxiliary ground conductor disposed along the transmissiondirection and connected to the plurality of ground conductors, in theouter edge portion of the parallel extending portion.
 14. The multilayerboard according to claim 1, wherein the laminated insulating bodyincludes a resist covering one of the plurality of ground conductors.